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Thread: Why is it still the Theory of Relativity?

  1. #1 Why is it still the Theory of Relativity? 
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    Hasn't relativity been proven? Why is it still referred to as a theory?
    Could it be that it is because relativity cannot be measured?

    FW


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  3. #2 Re: Why is it still the Theory of Relativity? 
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    Quote Originally Posted by fw2008
    Hasn't relativity been proven? Why is it still referred to as a theory?
    Could it be that it is because relativity cannot be measured?

    FW
    Your assertion shows that you don't fully appreciate what "theory" means in science. Theories aren't "proven" in the same sense as mathematical theorems.. They can be verified to a degree of accuracy, but it is always possible that some experiment will point up a discrepancy.

    In the case of speical relativity, so far all tests have been in agreement with the theory.
    For general relativity, there is a problem in reconciling it with quantum theory in situations where both need to apply - the best example is what is going on inside a black hole?


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    In empirical sciences like physics, a theory is the highest confidence level a paradigm can achieve. Following Karl Popper and other relevant philosophers, a scientific hypothesis cannot be proved. You only gain more confidence with every new experimental agreement with the predictions of a hypothesis that eventually becomes a theory. Therefore, it is very important that a scientific theory must in principle be capable of being falsified. Because every single disagreement with the prediction of a theory or hypothesis immediately means it is wrong. Depending on the severity of this disagreement, it leads to modifications or even total disapproval. The former reaction can be regarded an evolutionary, the latter a revolutionary progress in science. This is also the reason, why some so-called theories are useless, i.e. unscientific, because they cannot be evaluated according to this scheme.

    Often, the validity of a theory depends on the boundary conditions. In general, the old Newtonian mechanics can be considered falsified, because they do not include relativistic effects. On the other hand, as long as certain boundary conditions are met (small velocities compared to light speed, large masses etc.) they are still valid and not distinguishable from predictions of the more general approaches of Special and General Relativity. In this sense, relativistic mechanics are an evolutionary step based on Newtonian mechanics. On the other hand, Relativity is also revolutionary, because the fundamental concepts are totally different.
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    In general, the old Newtonian mechanics can be considered falsified, because they do not include relativistic effects.
    As I understand it, relativity equations simplify to Newtonian mechanics under low velocities. Would it not then be pertinent to say that relativity is a more accurate version of Newtonian mechanics? I mean it in the sense that neither theory really knows how the things happen as they do, but they can predict the outcome of scenarios within their operating limits. If one day a unified theory is found, it would probably work in the same way, in that it would simplify to the relevant situation when the variables are entered. Am I seriously off base?
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    Quote Originally Posted by KALSTER
    In general, the old Newtonian mechanics can be considered falsified, because they do not include relativistic effects.
    As I understand it, relativity equations simplify to Newtonian mechanics under low velocities. Would it not then be pertinent to say that relativity is a more accurate version of Newtonian mechanics? I mean it in the sense that neither theory really knows how the things happen as they do, but they can predict the outcome of scenarios within their operating limits. If one day a unified theory is found, it would probably work in the same way, in that it would simplify to the relevant situation when the variables are entered. Am I seriously off base?
    No. It would be proper to say that Newtonian mechanics is good approximation to relativity when the speeds are low with respect to the speed of light and (taking relativity to mean general relativity) when gravitational fields are low to moderate.

    If a unified theory is every found it will have to conform to the correspondence principle. That means that it will have to agree closely (within experimental error) with general relativity in circumstances where general relativity is known to be accurate and it will have to agree with quantum field theory in the sub-atomic realm.
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    This is exactly, how I wanted to be understood. These are the "evolutionary" aspects. However, there are also more severe changes in the paradigm of understanding mechanics like the finite and constant speed of light as well as the concept of space-time and the idea that both space and time are not absolute. These things are not part of Newtonian mechanics or even contradict parts of its conceptual design. Predicting experimental results within certain degrees of accuracy is one thing, having a certain of picture of how Nature works is another.

    My standard example is the atomic model of Bohr describing the interior of an atom similar to a planetary system. Although it is entirely wrong, as we know today (cf. wave particle duality, uncertainty principle, etc.), it provides very precise results in the case of a hydrogen atom. Isn't this exactly, what the verification and falsification of scientific theories is about? They are considered being correct as long as there are no contradictions. We are now in the bizarre situation that we know that relativistic mechanics and quantum mechanics are not compatible, although they seem to be applicable in their individual domains. And as long as we cannot combine both realms, we have to live with what we have, but we can be very certain that as long as we stay within those boundaries, the results we get are correct.
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    Quote Originally Posted by Dishmaster
    This is exactly, how I wanted to be understood. These are the "evolutionary" aspects. However, there are also more severe changes in the paradigm of understanding mechanics like the finite and constant speed of light as well as the concept of space-time and the idea that both space and time are not absolute. These things are not part of Newtonian mechanics or even contradict parts of its conceptual design. Predicting experimental results within certain degrees of accuracy is one thing, having a certain of picture of how Nature works is another.

    My standard example is the atomic model of Bohr describing the interior of an atom similar to a planetary system. Although it is entirely wrong, as we know today (cf. wave particle duality, uncertainty principle, etc.), it provides very precise results in the case of a hydrogen atom. Isn't this exactly, what the verification and falsification of scientific theories is about? They are considered being correct as long as there are no contradictions. We are now in the bizarre situation that we know that relativistic mechanics and quantum mechanics are not compatible, although they seem to be applicable in their individual domains. And as long as we cannot combine both realms, we have to live with what we have, but we can be very certain that as long as we stay within those boundaries, the results we get are correct.
    Absolutely correct. Approximation of Newtonian mechanics to relativity illustrates two important aspects of the correspondence principle

    First, relativity when it replaced Newtonian mechanics was required to provide predictions that are in close agreement with Newtonian mechanics for low speeds and moderate gravitational fields. It is the predictions that must reduce to the known theory (in this case of Newtonian mechanics).

    Second, the overall model and the mechanisms and perceptions that go along with relativity are totally different than the models that go with Newtonian mechanics -- constancy of the speed of light, relativity of time, etc. So in that sense relativity was a complete and total departure from Newton's theory. Philosophically the theories are totally different.

    Similarly, if an when there is a unified theory of gravity and quantum theory, a "Theory of Everything" it is quite likely that it will bear little resemblance to either theory in the perspective that if affords on the mechanisms at work in the uiverse. It will of necessity provide very close predictions in the appropriate circumstances, but the means by which it provides those predictions may appear quite alien from the perspective of either quantum field theory or of general relativity.
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  9. #8  
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    Quote Originally Posted by DrRocket
    Second, the overall model and the mechanisms and perceptions that go along with relativity are totally different than the models that go with Newtonian mechanics -- constancy of the speed of light, relativity of time, etc. So in that sense relativity was a complete and total departure from Newton's theory. Philosophically the theories are totally different.
    True. For example, action-at-a-distance was key to Newtons laws as was the speed of light which had to be instantaneous, but these are not consistent with relativity or what has been measured.
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